If it were me, I'd have the whole thing media blasted, then coated in a professional spray-on truck bed coating such as LineX or Rhinelining. There really isn't anything tougher than that, and they are MUCH thicker coatings (you could even ask to have them sprayed thicker than usual). Coating like this is what've done with other aftermarket stuff like bumpers, roll bars, nerf bars, etc....
